Add explicit EOF to top-level parser rule (#1217) (#1250)

* Fixes #1154
* Tests that #1154 example produces SyntaxErrorsException
* Generally helps catch trailing syntax errors
* Performance-neutral relative to previous grammar
* Recommended by antlr4 devs, can help performance in some cases
* See antlr/antlr4#1540

(cherry picked from commit 8f108c1a)